The invention relates to a method for compensating load produced deflections in a roll, and to rolls in which said method is applied.
Several methods are known for compensating load produced roll deflections. In rolls, having a shaft functionally separated from the roll mantle by means of bearings, the following basic types of deflection compensation can be mentioned, all based mainly on the use of hydraulic control means.
A first group comprises rolls, in which a counter force is produced in the central portion of the roll for preventing deflection of the roll mantle. Then the outermost bearings between the shaft and the mantle are rigidly attached. Constructions of this kind are shown in patent publications GB No. 893 426 and DE No. 1 231 660, FIG. 2.
A second group comprises rolls, in which the counter force is produced by means of a pressure medium element extending all along the roll. In equivalent arrangements there are several pressure medium elements, each associated with a specific bearing, and all connected to a common pressure source. Constructions of this kind are shown in patent publication DE No. 1 561 732 and in FIG. 1 of the previously mentioned patent publication DE No. 1 231 660.
A third group comprises rolls, broadly of the same kind as in the first group, in which the pressure generated can be controlled individually for each bearing. A construction of this kind is shown in patent publication U.S. Pat. No. 3,389,450.
A common feature in all known solutions is the generation of a counter force objecting deflection of the roll mantle. In order to obtain a satisfactory deflection compensation in this manner, the counter force should be selectively controllable at different points of the roll mantle, because variations in the load require corresponding adjustment of the counter force. Constructions allowing such a selective force adjustment tend to become extremely complicated and expensive.
The object of the invention is to eliminate the drawbacks of the known constructions and to create a simple and reliable deflection compensation system. By applying the method according to the invention, the roll can be kept constructionally uncomplicated. When the flexible elements used in the roll are suitably adapted to the roll stiffness, the roll will be self-adjusting. Hence, there is no need for adjustment to meet load variations.
Usually the aim is to keep the mantle of a roll as straight as possible under load. This can be obtained by prestressing, preferably hydraulically, each of the flexible elements to a tension corresponding to the stiffness of the shaft. Such a prestress can favourably be used also when the roll mantle is not supposed to be completely linear under load, but to have a certain curved form. This is feasible, for example, if a conform line pressure is desired in a roll nip, where the counter roll has a slightly curved form.
A favourable design with regard to the adjustment procedure as well as service requirements is obtained, by locating the flexible elements so, that they allow radial yielding motion between the actual bearing unit and the shaft. A particularly uncomplicated and favourable construction is obtained by providing the roll, at its central portion, with at least one rigidly attached bearing unit.
The invention also relates to a deflection control roll, which is made by applying the disclosed method. The characterizing features and the constructional details of such a roll are illustrated in the attached drawing and set forth in the detailed description.